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Commit 22426258 authored by Juri Lelli's avatar Juri Lelli Committed by Greg Kroah-Hartman
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cgroup/cpuset: Change cpuset_rwsem and hotplug lock order 



commit d74b27d63a8bebe2fe634944e4ebdc7b10db7a39 upstream.

commit 1243dc518c9da ("cgroup/cpuset: Convert cpuset_mutex to
percpu_rwsem") is performance patch which is not backport. So
convert percpu_rwsem to cpuset_mutex.

commit aa44002e ("cpuset: Fix unsafe lock order between
cpuset lock and cpuslock") makes lock order keep cpuset_mutex
->cpu_hotplug_lock. We should change lock order in cpuset_attach.

original commit message:

cpuset_rwsem is going to be acquired from sched_setscheduler() with a
following patch. There are however paths (e.g., spawn_ksoftirqd) in
which sched_scheduler() is eventually called while holding hotplug lock;
this creates a dependecy between hotplug lock (to be always acquired
first) and cpuset_rwsem (to be always acquired after hotplug lock).

Fix paths which currently take the two locks in the wrong order (after
a following patch is applied).

Tested-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Cc: claudio@evidence.eu.com
Cc: lizefan@huawei.com
Cc: longman@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: mathieu.poirier@linaro.org
Cc: rostedt@goodmis.org
Cc: tj@kernel.org
Cc: tommaso.cucinotta@santannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-7-juri.lelli@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarCai Xinchen <caixinchen1@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8ed4c825

include/linux/cpuset.h

+4 −4
Original line number Diff line number Diff line
@@ -40,14 +40,14 @@ static inline bool cpusets_enabled(void) 


static inline void cpuset_inc(void)

{

	static_branch_inc(&cpusets_pre_enable_key);

	static_branch_inc(&cpusets_enabled_key);

	static_branch_inc_cpuslocked(&cpusets_pre_enable_key);

	static_branch_inc_cpuslocked(&cpusets_enabled_key);

}



static inline void cpuset_dec(void)

{

	static_branch_dec(&cpusets_enabled_key);

	static_branch_dec(&cpusets_pre_enable_key);

	static_branch_dec_cpuslocked(&cpusets_enabled_key);

	static_branch_dec_cpuslocked(&cpusets_pre_enable_key);

}



extern int cpuset_init(void);

kernel/cgroup/cpuset.c

+17 −7
Original line number Diff line number Diff line
@@ -830,8 +830,8 @@ static void rebuild_sched_domains_locked(void) 
	cpumask_var_t *doms;

	int ndoms;



	lockdep_assert_cpus_held();

	lockdep_assert_held(&cpuset_mutex);

	get_online_cpus();



	/*

	 * We have raced with CPU hotplug. Don't do anything to avoid
@@ -839,15 +839,13 @@ static void rebuild_sched_domains_locked(void) 
	 * Anyways, hotplug work item will rebuild sched domains.

	 */

	if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))

		goto out;

		return;



	/* Generate domain masks and attrs */

	ndoms = generate_sched_domains(&doms, &attr);



	/* Have scheduler rebuild the domains */

	partition_sched_domains(ndoms, doms, attr);

out:

	put_online_cpus();

}

#else /* !CONFIG_SMP */

static void rebuild_sched_domains_locked(void)
@@ -857,9 +855,11 @@ static void rebuild_sched_domains_locked(void) 


void rebuild_sched_domains(void)

{

	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	rebuild_sched_domains_locked();

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

}



/**
@@ -1528,13 +1528,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
	cgroup_taskset_first(tset, &css);

	cs = css_cs(css);



	mutex_lock(&cpuset_mutex);



	/*

	 * It should hold cpus lock because a cpu offline event can

	 * cause set_cpus_allowed_ptr() failed.

	 */

	get_online_cpus();

	mutex_lock(&cpuset_mutex);



	/* prepare for attach */

	if (cs == &top_cpuset)

		cpumask_copy(cpus_attach, cpu_possible_mask);
@@ -1553,7 +1553,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);

		cpuset_update_task_spread_flag(cs, task);

	}

       put_online_cpus();



	/*

	 * Change mm for all threadgroup leaders. This is expensive and may
@@ -1589,6 +1588,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
		wake_up(&cpuset_attach_wq);



	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

}



/* The various types of files and directories in a cpuset file system */
@@ -1617,6 +1617,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, 
	cpuset_filetype_t type = cft->private;

	int retval = 0;



	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs)) {

		retval = -ENODEV;
@@ -1654,6 +1655,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, 
	}

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	return retval;

}
@@ -1664,6 +1666,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, 
	cpuset_filetype_t type = cft->private;

	int retval = -ENODEV;



	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs))

		goto out_unlock;
@@ -1678,6 +1681,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, 
	}

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	return retval;

}
@@ -1716,6 +1720,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 
	kernfs_break_active_protection(of->kn);

	flush_work(&cpuset_hotplug_work);



	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs))

		goto out_unlock;
@@ -1741,6 +1746,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 
	free_trial_cpuset(trialcs);

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	kernfs_unbreak_active_protection(of->kn);

	css_put(&cs->css);

	flush_workqueue(cpuset_migrate_mm_wq);
@@ -1985,6 +1991,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css) 
	if (!parent)

		return 0;



	get_online_cpus();

	mutex_lock(&cpuset_mutex);



	set_bit(CS_ONLINE, &cs->flags);
@@ -2035,6 +2042,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css) 
	spin_unlock_irq(&callback_lock);

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	return 0;

}
@@ -2048,6 +2056,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) 
{

	struct cpuset *cs = css_cs(css);



	get_online_cpus();

	mutex_lock(&cpuset_mutex);



	if (is_sched_load_balance(cs))
@@ -2057,6 +2066,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) 
	clear_bit(CS_ONLINE, &cs->flags);



	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

}



static void cpuset_css_free(struct cgroup_subsys_state *css)